Circular waveguide has recently been developed for providing a vertical feed to antennas for UHF broadcast television. In contrast to rectangular waveguide of comparable size, circular waveguide is easily pressurizable to two pounds per square inch to prevent hydration, and circular waveguide prevents a uniform profile so that wind loading is independent of direction. Circular waveguide also offers lower attenuation and higher power handling capability.
Similar improvements should be obtained if circular waveguide is also used for the horizontal run from the transmitting station to the base of the antenna tower. This presents a difficulty, however, in connecting or bending from the horizontal section of circular waveguide to the vertical section of waveguide feeding upwardly to the antenna. It is easy, for example, to use rectangular waveguide and a 90.degree. rectangular bend since it is well known that a rectangular waveguide can be distorted into a bend without a radical effect on either the cutoff frequency or general field configuration of the dominant TE.sub.10 mode in the bend. Manufacturing tolerances for a right angle bend using rectangular waveguide are not extreme so long as the bend takes place gradually. Even at UHF frequencies wherein the waveguide dimensions are on the order of 13 to 17 inches, a right angle bend using rectangular waveguide is easily obtained since the faces of the rectangular waveguide bend are easily fabricated from flat sheet metal. In contrast, a gradual bend using circular waveguide requires rather tight manufacturing tolerances to avoid unwanted reflections and signal distortion.